1. Field of the Invention
The present invention relates to a molten metal injector and, more particularly, a molten metal injector for use with a molten metal supply system and method of operating the same.
2. Description of the Prior Art
The metal working process known as extrusion involves pressing metal stock (ingot or billet) through a die opening having a predetermined configuration in order to form a shape having a longer length and a substantially constant cross-section. For example, in the extrusion of aluminum alloys, the aluminum stock is preheated to the proper extrusion temperature. The aluminum stock is then placed into a heated cylinder. The cylinder utilized in the extrusion process has a die opening at one end of the desired shape and a reciprocal piston or ram having approximately the same cross-sectional dimensions as the bore of the cylinder. This piston or ram moves against the aluminum stock to compress the aluminum stock. The opening in the die is the path of least resistance for the aluminum stock under pressure. The aluminum stock deforms and flows through the die opening to produce an extruded product having the same crosssectional shape as the die opening.
Referring to FIG. 1, the foregoing described extrusion process is identified by reference numeral 10, and typically consists of several discreet and discontinuous operations including: melting 20, casting 30, homogenizing 40, optionally sawing 50, reheating 60, and, finally, extrusion 70. The aluminum stock is cast at an elevated temperature and typically cooled to room temperature. Because the aluminum stock is cast, there is a certain amount of inhomogeneity in the structure and the aluminum stock is heated to homogenize the cast metal. Following the homogenization step, the aluminum stock is cooled to room temperature. After cooling, the homogenized aluminum stock is reheated in a furnace to an elevated temperature called the preheat temperature. Those skilled in the art will appreciate that the preheat temperature is generally the same for each billet that is to be extruded in a series of billets and is based on experience. After the aluminum stock has reached the preheat temperature, it is ready to be placed in an extrusion press and extruded.
All of the foregoing steps relate to practices that are well known to those skilled in the art of casting and extruding. Each of the foregoing steps is related to metallurgical control of the metal to be extruded. These steps are very cost intensive, with energy costs incurring each time the metal stock is reheated from room temperature. There are also in-process recovery costs associated with the need to trim the metal stock, labor costs associated with process inventory, and capital and operational costs for the extrusion equipment.
Attempts have been made in the prior art to design an extrusion apparatus that will operate directly with molten metal. U.S. Pat. No. 3,328,994 to Lindemann discloses one such example. The Lindemann patent discloses an apparatus for extruding metal through an extrusion nozzle to form a solid rod. The apparatus includes a container for containing a supply of molten metal and an extrusion die (i.e., extrusion nozzle) located at the outlet of the container. A conduit leads from a bottom opening of the container to the extrusion nozzle. A heated chamber is located in the conduit leading from the bottom opening of the container to the extrusion nozzle and is used to heat the molten metal passing to the extrusion nozzle. A cooling chamber surrounds the extrusion nozzle to cool and solidify the molten metal as it passes therethrough. The container is pressurized to force the molten metal contained in the container through the outlet conduit, heated chamber and, ultimately, the extrusion nozzle.
U.S. Pat. No. 4,075,881 to Kreidler discloses a method and device for making rods, tubes, and profiled articles directly from molten metal by extrusion through use of a forming tool and die. The molten metal is charged into a receiving compartment of the device in successive batches that are cooled so as to be transformed into a thermalplastic condition. The successive batches build up layer by layer to form a bar or other similar article.
U.S. Pat. Nos. 4,774,997 and 4,718,476 both to Eibe disclose an apparatus and method for continuous extrusion casting of molten metal. In the apparatus disclosed by the Eibe patents, molten metal is contained in a pressure vessel that may be pressurized with air or an inert gas such as argon. When the pressure vessel is pressurized, the molten metal contained therein is forced through an extrusion die assembly. The extrusion die assembly includes a mold that is in fluid communication with a downstream sizing die. Spray nozzles are positioned to spray water on the outside of the mold to cool and solidify the molten metal passing therethrough. The cooled and solidified metal is then forced through the sizing die. Upon exiting the sizing die, the extruded metal in the form of a metal strip is passed between a pair of pinch rolls and further cooled before being wound on a coiler.
In view of the foregoing, an object of the present invention is to provide an injector that is configured to operate directly with molten metal and may be used as part of a molten metal supply system for supplying molten metal to downstream metalworking or forming processes. A further object of the present invention is to provide an injector having the benefit of greatly reduced wear between its moving parts and the ability to generate relatively high working pressures with correspondingly small amounts of stored energy.
The foregoing objects are accomplished with an injector for a molten metal supply system and method of operating the same in accordance with the present invention. The injector includes an injector housing configured to contain molten metal. A molten metal supply source is in fluid communication with the housing. A piston is reciprocally operable within the housing. The piston is movable through a return stroke allowing molten metal to be received into the housing from the molten metal supply source, and a displacement stroke for displacing the molten metal from the housing to a downstream process. The piston has a pistonhead for displacing the molten metal from the housing. A gas supply source is in fluid communication with the housing through a gas control valve. The injector is operable such that during the return stroke of the piston a space is formed between the pistonhead and the molten metal and the gas control valve is operable to fill the space with gas from the gas supply source. The injector is further operable such that during the displacement stroke of the piston the gas control valve is operable to prevent venting of gas from the gas filled space such that the gas in the gas filled space is compressed between the pistonhead and molten metal received into the housing and displaces the molten metal from the housing ahead of the pistonhead.
The piston may include a piston rod having a first end and a second end. The first end may be connected to the pistonhead and the second end may connected to an actuator for driving the piston through the return stroke and the displacement stroke. The second end of the piston may be connected to the actuator by a self-aligning coupling. An annular pressure seal may be located about the piston rod to provide a substantially gas tight seal between the piston rod and the housing. A cooling water jacket may be positioned about the housing substantially coincident with the pressure seal for cooling the pressure seal. The first end of the piston rod may be connected to the pistonhead by a thermal insulation barrier. The piston rod may define a central bore that is in fluid communication with a cooling water inlet and outlet for supplying cooling water to the central bore in the piston rod.
The housing and piston rod may be made of high temperature resistant metal alloy. The pistonhead may be made of high temperature resistant metal alloy, refractory material, or graphite. The housing may include a refractory material liner or a graphite liner. The molten metal supply source may be a supply of molten aluminum, magnesium, copper, bronze, iron, and alloys thereof. The gas supply source may consist of helium, nitrogen, argon, compressed air, or carbon dioxide.
The injector may further include a floating thermal insulation barrier located between the pistonhead and the molten metal received into the housing. The floating barrier preferably remains substantially in contact with the molten metal throughout the return and displacement strokes of the piston. The injector may further include an injection port connected to the housing for injecting the molten metal displaced from the housing to the downstream process. The molten metal supply source may be in fluid communication with the housing through a check valve, which may be located in the injection port. A second check valve may be located in the injection port and configured to allow the displacement of molten metal from the housing.
The injector of the present invention may be configured to operate with a liquid medium rather than a gas medium. The injector, according to a second embodiment of the present invention, also includes an injector housing configured to contain molten metal. A molten metal supply source is in fluid communication with the housing. A liquid chamber is positioned above and in fluid communication with the housing. The liquid chamber contains a liquid chemically resistive to the molten metal contained in the molten metal supply source. A piston is reciprocally operate within the housing. The piston is movable through a return stroke allowing molten metal to be received into the housing from the molten metal supply source, and a displacement stroke for displacing the molten metal from the housing. The piston has a pistonhead for displacing the molten metal from the housing. The liquid chamber is in fluid communication with the housing such that during the return and displacement strokes of the piston, liquid from the liquid chamber is located about the pistonhead and between the molten metal received into the housing and the liquid chamber.
The liquid in the liquid chamber is preferably a viscous liquid such as boron oxide. The liquid chamber may be positioned directly on top of the housing and the piston may be reciprocally operable such that during the return stroke of the piston, the pistonhead retracts at least partially upward into the liquid chamber. The pistonhead may define a circumferentially extending recess, with the recess filled with liquid from the liquid chamber during the return and displacement strokes.
The present invention is further directed to a method of operating an injector for a molten metal supply system that may include the steps of: providing an injector having an injector housing configured to contain molten metal and a piston reciprocally operable within the housing, with the piston movable through a return stroke and a displacement stroke, with the piston having a pistonhead located within the housing, and with the housing in fluid communication with a molten metal supply source and a gas supply source; receiving molten metal from the molten metal supply source into the housing during the return stroke of the piston, with the pistonhead defining a space with the molten metal flowing into the housing; filling the space with gas from the gas supply source during the return stroke of the piston; and compressing the gas in the gas filled space between the pistonhead and the molten metal received into the housing during the displacement stroke of the piston to displace the molten metal from the housing to a downstream process in advance of the compressed gas.
The method may further include the step of venting the compressed gas in the gas filled space to atmospheric pressure approximately when the piston reaches the end of the displacement stroke. In addition, the method may further include the steps of: moving the piston through a partial return stroke in the housing after the step of compressing the gas in the gas filled space to partially relieve the pressure in the compressed gas filled space; venting the gas in the gas filled space to atmospheric pressure with the piston located at about the end of the partial return stroke in the housing; and returning the piston substantially to the end of the displacement stroke position in the housing.
When the injector is configured to operate with a liquid medium, the method according to the present invention may include the steps of: providing an injector having an injector housing configured to contain molten metal and a piston positioned to extend at least partially into the housing and reciprocally operate within the housing, with the piston movable through a return stroke and a displacement stroke, and with the piston having a pistonhead, with the housing in fluid communication with a molten metal supply source, and with the housing in fluid communication with a liquid chamber located above the housing and containing a liquid chemically resistive to the molten metal contained in the molten metal supply source; receiving molten metal from the molten metal supply source into the housing during the return stroke of the piston; supplying liquid from the liquid chamber around the pistonhead and between the molten metal received into the housing and the liquid chamber; and moving the piston through the displacement stroke to displace the molten metal from the housing to a downstream process. The liquid chamber is preferably in fluid communication with the housing such that during the return and displacement strokes of the piston, liquid from the liquid chamber is located around the pistonhead and between the molten metal received into the housing and the liquid chamber.